Influence of the auxiliary acceptor and π-bridge in carbazole dyes on photovoltaic properties

Article abstract of DOI:10.1016/j.jphotochem.2016.08.033

Six N-dimethylfluorenylcarbazole dyes have been synthesized based on benzene, furan and thiophene π-bridge with or without benzothiadiazole auxiliary acceptor. Their photophysical properties and photovoltaic performance are investigated systematically based on the incorporation of benzothiadiazole and the variety of π-bridges. The presence of benzothiadiazole broadens the absorption spectra and favors the light-harvesting abilities, which benefits better IPCE spectra and accordingly improved J_SC. In addition, benzothiadiazole plays a role on the effects of π-bridge on the photoelectrical conversion efficiency. Dye bearing thiophene bridge achieves optimal photovoltaic performance 4.14% among those carbazole dyes without benzothiadiazole while when with benzothiadiazole dye bearing furan bridge exhibits the best cell efficiency 4.96% under AM 1.5G condition (N719 dye's 6.57% under the same condition).

Full text of DOI:10.1016/j.jphotochem.2016.08.033

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Journal of Photochemistry and Photobiology A: Chemistry 332 (2017) 283–292
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Influence of the auxiliary acceptor and
p-bridge in carbazole dyes on
photovoltaic properties
*
Yang Liu, Ji He, Liang Han , Jianrong Gao
College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310032, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Six N-dimethylfluorenylcarbazole dyes have been synthesized based on benzene, furan and thiophene
-bridge with or without benzothiadiazole auxiliary acceptor. Their photophysical properties and
photovoltaic performance are investigated systematically based on the incorporation of benzothiadia-
zole and the variety of -bridges. The presence of benzothiadiazole broadens the absorption spectra and
favors the light-harvesting abilities, which benefits better IPCE spectra and accordingly improved JSC. In
addition, benzothiadiazole plays a role on the effects of -bridge on the photoelectrical conversion
efficiency. Dye bearing thiophene bridge achieves optimal photovoltaic performance 4.14% among those
carbazole dyes without benzothiadiazole while when with benzothiadiazole dye bearing furan bridge
exhibits the best cell efficiency 4.96% under AM 1.5G condition (N719 dye’s 6.57% under the same
condition).
Received 1 June 2016
Received in revised form 31 July 2016
Accepted 30 August 2016
Available online 9 September 2016
p
p
Keywords:
Carbazole sensitizer
Benzothiadiazole
p
p
-Bridge
Synthesis
Photovoltaic performance
ã 2016 Elsevier B.V. All rights reserved.
1. Introduction
system. Various donors and p-bridges are introduced in the
molecular engineering of metal-free organic sensitizers to improve
the spectral properties and photovoltaic performance [9–13]. The
incorporation of another auxiliary acceptor is also an efficient
Crystalline silicon solar cell is the main representative of the
solar energy utilization, which has a mature application technolo-
gy and high market share [1]. However, the requirement of
ultrapure silicon single crystals promotes the improvement of
alternative photovoltaic solar cells [2]. Dye-sensitized solar cell
(DSSC), a promising environmentally friendly photovoltaic device
for converting sunlight to electricity, has aroused a lot of attention
due to their low material cost, flexibility, easy manufacturing
process and high photovoltaic performance [3].
In DSSC, the light-harvesting ability and electron injection
efficiency of dye molecules are the determining factors for the
photoelectrical conversion performance. The possibility of im-
proving the photovoltaic performance through small change of the
molecular structure raises the diverse design for metal-free
organic sensitizers [4–7]. Metal-free organic sensitizer is charac-
terized with high molar extinction coefficient, wide absorptive
spectrum and low cost, which help it win the superiority to metal
organic sensitizer [8]. A typical structure of metal-free organic
design concept and D-A-p-A-based sensitizers have witnessed
considerable progress in the enhancement of the photovoltaic
performance [14]. The presence of another electron-deficient
acceptor may not only facilitate intramolecular charge transfer
(ICT) thus enhancing the light harvesting ability, but also decrease
the energy level of LUMO orbital improving the dye photostability,
which contribute to most efficient and stable sensitizers for DSSC
application [15]. In 2012, Zhu et al. reported an indoline sensitizer
bearing benzothiadiazole acceptor with power conversion effi-
ciency 9.04% [16]; Kim et al. synthesized three triarylamine
sensitizers based on thieno[3,2-b][1]benzothiophene unit and
found a triarylamine sensitizer with benzothiadiazole-phenyl unit
exhibits a better photoelectrical conversion efficiency 10.47% than
that with benzothiadiazole- thiophene unit [17].
Among the common used auxiliary acceptor, benzothiadiazole
(BTZ) with good electron-withdrawing ability is an extensively
sensitizer is composed of an electron donor, a
p
-bridge and an
exploited acceptor in the design of D-A-
outstanding long-term stability is observed in the benzothiadia-
zole-based D-A- -A sensitizers [18]. We ever reported D-A- -A
p-A sensitizers and
electron acceptor arranged in a donor-
p
-bridge-acceptor (D- -A)
p
p
p
carbazole sensitizers ZXY-1–ZXY-4 by incorporating benzothia-
diazole into carbazole dyes [19]. It is found ZXY-3 with benzene
bridge gives better photoelectrical conversion efficiency than ZXY-
* Corresponding author.
E-mail address: hanliang814@163.com (L. Han).
http://dx.doi.org/10.1016/j.jphotochem.2016.08.033
1010-6030/ã 2016 Elsevier B.V. All rights reserved.

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Y. Liu et al. / Journal of Photochemistry and Photobiology A: Chemistry 332 (2017) 283–292
1 with thiophene bridge. In fact,
photovoltaic performance in the design of new sensitizers, which
plays a key role in intramolecular charge transfer. Benzene and
p
-bridge is crucial to the
frequency ranged from 100 mHz to 1 MHz while the AC amplitude
was set to 10 mV. The bias of all EIS measurements was set to the
VOC of the corresponding dyes.
five-member heterocycles are the common used
p-bridges and
usually benzene benefits the photovoltage while furan and
thiophene favor the photocurrent [20–23]. The ultimate cell
2.4. General procedure for the synthesis of compounds
efficiency is determined by the combined effect of
the rest of the molecule.
p
-bridge and
2.4.1. Synthesis of 9-(9,9-dimethyl-9H-fluoren-2-yl)-9H-carbazole I
To a solution of carbazole (2.00 g, 12 mmol) and 2-bromo-9,9-
dimethyl-9H-fluorene (2.73 g, 10 mmol) in dry and degassed
xylene (60 mL) were added Pd(OAc)2 (0.07 g, 0.30 mmol), P(t-
Carbazole and their derivatives are characterized with
electron-rich property and good hole-transporting capability,
which have been used as electroluminescent, non-linear optical
(NLO) and photorefractive materials [24]. In addition, electron-
rich and bulky fluorene units [25] are always used in the
sensitizers to enhance the electron-donating ability of the donor
and suppress the charge recombination. Therefore, in order to
further improve the photovoltaic performance and investigate
the principle of molecular engineering, we synthesized six N-
dimethylfluorenylcarbazole dyes based on different aryl bridges
with or without benzothiadiazole and investigated the relation-
ship between the structure of carbazole dyes and the photovoltaic
performance.
Bu)3 HBF4 (0.29 g, 1.00 mmol), Cs2CO3 (9.75 g, 30 mmol). The
ꢁ
mixture was refluxed for 15 h under N2 atmosphere. After the
reaction was finished, the mixture was cool down to room
temperature and filtered. The filtrate was concentrated to dryness
and the residue was purified with silica-gel column chromatogra-
phy (petroleum) to afford compound I as a white solid (3.02 g,
84%), m.p. 123.5–124.5 ꢀC. 1H NMR (500 MHz, CDCl3)
d 8.20 (d,
J = 7.8 Hz, 2H), 7.95 (d, J = 7.9 Hz, 1H), 7.83 (d, J = 6.9 Hz, 1H), 7.66 (d,
J = 1.7 Hz, 1H), 7.57 (dd, J = 7.9, 1.8 Hz, 1H), 7.51 (t, J = 9 Hz, 3H), 7.46
(t, J = 7.2 Hz, 2H), 7.42 (t, J = 8 Hz, 2H), 7.33 (t, J = 7.2 Hz, 2H), 1.59 (s,
6H).
2. Experimental
2.4.2. Synthesis of 3-bromo-9-(9,9-dimethyl-9H-fluoren-2-yl)- 9H-
carbazole II
2.1. Materials and characterization
Compound II was synthesized in DMF through the similar
method reported by Ref [26] as a white solid (0.43 g, 98%). m.p. 94–
96 ꢀC.
Nuclear magnetic resonance spectra were recorded on Bruker
Avance III 500 MHz and chemical shifts are expressed in ppm using
TMS as an internal standard. Mass spectra were measured using a
Waters Xevo Q-Tof Mass Spectrometer. Absorption spectra were
measured with SHIMADZU (model UV2550) UV–vis spectropho-
tometer. Fluorescence spectra were obtained on a SHIMADZU RF-
5301PC spectrofluorometer.
2.4.3. Synthesis of 3-(7-bromo-2,1,3-benzothiadiazol-4-yl)-9-(9,9-
dimethyl-9H- fluoren-2-yl)- 9H-carbazole III
The solution of II (4 g, 9.12 mmol) in anhydrous THF (50 mL) was
cooled to ꢂ78 ꢀC, and then n-BuLi (6.84 mL, 10.9 mmol, 1.6 mol/L in
hexane) was added dropwisely. The reactant was stirred for 1 h and
then trimethyl borate (1.56 mL, 13.68 mmol) was added at once.
The mixture was allowed to warm to room temperature and stirred
for 20 h. The obtained solution was used directly in the subsequent
Suzuki coupling without further treatment.
2.2. Fabrication of DSSCs
The FTO glass was first cleaned in a detergent solution using an
ultrasonic bath for 15 min, and then rinsed with water and ethanol.
For the fabrication of photoelectrodes, titanium nanoxide paste
was deposited by screen-printing, resulting in the TiO2 electrodes.
Under
a
nitrogen atmosphere, benzothiadiazole(3.0 g,
10.2 mmol), Pd(PPh3)4 (1.17 g, 1.02 mmol) and aqueous K2CO3
(19 mL, 2 mol/L) were dissolved in THF (60 mL). After the reactant
was refluxed for 14 h, the mixture was extracted with CH2Cl2 and
washed with water. The combined organic layer was dried over
NaSO4, filtered and concentrated. The residue was purified by
column chromatography (VPE:VEA = 5:1) to give compound III as a
yellow solid (2.97 g, 50.8%). m.p. 199 ꢃ 202 ꢀC; 1H NMR (500 MHz,
The thickness of TiO2 film was 12 mm. The TiO2 electrodes were
gradually heated under an air flow at 325 ꢀC for 5 min, at 375 ꢀC for
5 min, and at 450 ꢀC for 15 min, and finally, at 500 ꢀC for 15 min.
After being cooled to 80 ꢀC, the TiO2 electrode was immersed into
the dye solution in a mixture of MeOH and CHCl3 (VMeOH
:
V
CHCl3 = 1:10) and kept at room temperature for 24 h to assure
CDCl3) d 8.70 (d, J = 1.4 Hz, 1H), 8.26 (d, J = 7.8 Hz, 1H), 8.01 (dd,
complete dye uptake, which were then rinsed with MeOH to
remove excess dye. Meanwhile, the counter electrodes were
prepared by screen-printing a 50 nm Pt layer on the cleaned FTO
plates. Open cells were fabricated in air by clamping the different
photoelectrodes with platinized counter electrodes. The electro-
lyte used here is composed of the CH3CN solution of 0.3 M 1,2-
dimethyl-3-propylimidazolium iodide (DMPII), 0.03 M I2, 0.07 M
LiI, 0.1 M guandine thiocyanate, and 0.4 M 4-tert-butylpytiding
(TBP). The active area of DSSCs was 0.36 cm2.
J = 8.6, 1.8 Hz, 1H), 7.99 (d, J = 7.6 Hz, 1H), 7.97 (d, J = 8.0 Hz, 1H),
7.84 (dd, J = 6.5, 1.5 Hz, 1H), 7.72 (d, J = 7.6 Hz, 1H), 7.68 (d, J = 1.8 Hz,
1H), 7.62 (d, J = 8.5 Hz, 1H), 7.59 (dd, J = 7.9, 1.9 Hz, 1H), 7.54-7.47
(m, 3H), 7.45-7.39 (m, 2H), 7.36 (ddd, J = 7.9, 6.5, 1.6 Hz, 1H), 1.58
(s, 6H)
2.4.4. Synthesis of 5-[7-(9-(9,9-dimethyl-9i-fluoren-2-yl)-9H-
carbazol-3-yl)-2,1,3-benzothiadiazol-4-yl]- 2-
thiophenecarboxaldehyde IVa
A mixture of compound III (1.74 g, 3.04 mmol), (5-formylth-
iophen-2-yl)boronic acid (0.69 g, 4.4 mmol), Pd(PPh3)4 (0.35 g,
0.30 mmol), aqueous K2CO3 (2 M, 6 mL) inTHF (18 mL) was refluxed
for 10 h under N2 atmosphere. The reaction was quenched with
water. The reactant was extracted with dichloromethane and dried
over anhydrous Na2SO4. After removal of the solvent, the residue
was purified by column chromatography (VCH2Cl2: VPE = 2:1) to
afford compound IVa as a yellow solid (0.72 g, 40%). m.p. 243–
2.3. Photovoltaic characterization
The photovoltaic performance of the DSSCs was evaluated at
AM 1.5 G illumination (100 mW/cm2; Sol3A, Newport, USA) using a
Keithley digital source meter (Keithley 2420, USA). The action
spectra of monochromatic incident photon-to-current conversion
efficiency (IPCE) for solar cell were performed by a Hypermono-
light (SM-25, Jasco, Japan). Electrochemical impedance spectros-
244 ꢀC; 1H NMR (500 MHz, CDCl3)
d: 10.02 (s,1H), 8.80 (d, J = 1.5 Hz,
copy (EIS) experiments were conducted using
controlled potentiostat (ZeniumZahner, Germany). The measured
a
computer-
1H), 8.28-8.27 (m, 2H), 8.15 (d, J = 7.5 Hz,1H), 8.10 (dd, J = 8.6,1.8 Hz,
1H), 7.98 (d, J = 7.9 Hz, 1H), 7.93 (d, J = 7.5 Hz, 1H), 7.90 (d, J = 4.0 Hz,

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285
1H), 7.84 (dd, J = 6.8 Hz,1H), 7.69 (d, J = 1.8 Hz,1H), 7.64 (d, J = 8.6 Hz,
1H), 7.60 (dd, J = 8.0, 1.9 Hz, 1H), 7.53–7.48 (m, 3H), 7.46–7.40 (m,
2H), 7.40–7.35 (m, 1H), 1.60 (s, 6H).
118.59, 116.56, 114.91, 114.85, 109.90, 109.57, 98.39, 46.83, 26.61
(2C); IR n
/cmꢂ1 (KBr): 3451.83, 2925.84, 2222.59,1696.64, 1605.49,
1544.42, 1462.81, 1424.37, 1348.24, 1231.96, 1028.14, 808.31,
739.88; HRESIMS m/z 653.1653 [MꢂH]ꢂ, cacld C41H26N4O3S for:
654.1726; Elemental analysis calcd (%): C 75.21, H 4.00, N 8.56;
Found (%):C 75.30, H 4.32, N 8.95.
2.4.5. Synthesis of 2-cyano-3-[5-[7-(9-(9,9-dimethyl-9H-fluoren-2-
yl)-9H-carbazol-3-yl)-2,1,3-benzothiadiazol-4-yl]-2-thienyl]- 2-
propenoic acid LY-S
To a solution of compound IVa (0.2 g, 0.33 mmol) and cyano-
acetic acid (0.06 g, 0.7 mmol) in THF (20 mL), piperidine (0.16 mL)
was added. The mixture was refluxed for 12 h. Then the solvent
was removed in vacuo and the residue was purified by column
chromatography (VCH2Cl2: VCH3OH: VHAc = 400: 8: 2) to afford
compound LY-S as a purple solid (0.18 g, 80%). m.p. 269–271 ꢀC; 1H
2.4.8. Synthesis of 4-[7-(9-(9,9-dimethyl-9H-fluoren-2-yl)-9H-
carbazol-3-yl)-2,1,3-benzothiadiazol-4-yl]- benzaldehyde IVc
A mixture of compound III (0.2 g, 0.35 mmol), (4-formylphenyl)
boronic acid (0.11 g, 0.7 mmol), Pd(PPh3)4 (0.04 g, 0.035 mmol),
aqueous K2CO3 (2 M, 0.7 mL) in THF (18 mL) was refluxed for 10 h
under N2 atmosphere. The reaction was quenched with water. The
reactant was extracted with dichloromethane and dried over
anhydrous Na2SO4. After removal of the solvent, the residue was
purified by column chromatography (VCH2Cl2: VPE = 2:1) to afford
compound IVc as a yellow solid (0.13 g, 62%). m.p. 249–252 ꢀC; 1H
NMR (500 MHz, DMSO)
d: 8.99 (s, 1H), 8.57 (s, 1H), 8.44 (d,
J = 7.6 Hz,1H), 8.38 (dd, J = 7.8 Hz,1H), 8.34 (d, J = 4.1 Hz,1H), 8.20 (d,
J = 8.7 Hz, 1H), 8.17- 8.10 (m, 3H), 7.97 (d, J = 7.1 Hz, 1H), 7.94 (s, 1H),
7.65 (t, J = 8.8 Hz, 2H), 7.60 (d, J = 8.6 Hz, 1H), 7.55-7.48 (m, 2H),
7.45-7.40 (m, 2H), 7.37 (t, J = 7.4 Hz, 1H), 1.56 (s, 6H); 13C NMR
NMR (500 MHz, CDCl3) d: 10.15 (s, 1H,), 8.79 (d, J = 1.5 Hz, 1H), 8.28
(125 MHz, DMSO)
d
: 163.58, 155.28, 153.66, 153.09, 151.78, 147.57,
(d, J = 7.7 Hz, 1H), 8.23 (d, J = 8.2 Hz, 2H), 8.12-8.09 (m, 3H), 7.99 (d,
J = 2.7 Hz, 1H), 7.97 (d, J = 2.1 Hz, 1H), 7.95 (d, J = 7.3 Hz, 1H), 7.84 (d,
J = 7.0 Hz, 1H), 7.70 (d, J = 1.8 Hz, 1H), 7.65 (d, J = 8.5 Hz, 1H), 7.61 (dd,
J = 7.9,1.9 Hz,1H), 7.53-7.49 (m, 3H), 7.45-7.41 (m, 2H), 7.39-7.36 (m,
1H), 1.60 (s, 6H,).
146.27,140.71,140.24,139.62,139.54,138.01,137.73, 136.36,135.59,
134.24, 128.28, 127.70, 127.56, 127.45, 127.22, 126.54, 125.35,
122.97, 122.93, 122.83 (2C), 121.50, 121.27, 121.18, 121.13, 120.67,
120.35 (2C), 116.50, 109.91, 109.70, 98.64, 46.83, 26.61 (2C); IR
n
/cmꢂ1 (KBr): 3442.74, 2921.87, 2221.29, 1797.14, 1686.9, 1574.91,
1490.42, 1456.01, 1422.76, 1353.01, 1242.67, 885.43, 811.29, 738.00;
HRESIMS m/z 669.1456 [M-H]ꢂ, cacld C41H26N4O2S2 for: 670.1497;
Elemental analysis calcd (%): C 73.41, H 3.91, N 8.35; Found (%):C
73.70, H 3.97, N 8.25.
2.4.9. Synthesis of 2-cyano-3-[4-[7-(9-(9,9-dimethyl-9H-fluoren-2-
yl)-9H-carbazol-3-yl)-2,1,3-benzothiadiazol-4-yl]phenyl]- 2-
propenoic acid LY-P
To
a solution of compound IVc (0.2 g, 0.33 mmol) and
cyanoacetic acid (0.06 g, 0.7 mmol) in THF (20 mL), piperidine
(0.16 mL) was added. The mixture was refluxed for 12 h. Then the
solvent was removed in vacuo and the residue was purified by
column chromatography (VCH2Cl2: VCH3OH: VHAc = 400: 8: 2) to
afford compound LY-P as a purple solid (0.186 g, 84.5%). m.p.
2.4.6. Synthesis of 5-[7-(9-(9,9-dimethyl-9H-fluoren-2-yl)-9H-
carbazol-3-yl)-2,1,3-benzothiadiazol-4-yl]- 2-furancarboxaldehyde
IVb
A mixture of compound III (0.5 g, 0.875 mmol), (5-formylfuran-
2-yl)boronic
acid
(0.245 g,1.75 mmol),
Pd(PPh3)4
(0.1 g,
257 ꢃ259 ꢀC; 1H NMR (500 MHz, DMSO)
d 8.99 (d, J = 1.6 Hz, 1H),
0.0875 mmol), aqueous K2CO3 (2 M, 1.75 mL) in THF (18 mL) was
refluxed for 10 h under N2. The reaction was quenched with water.
The reactant was extracted with dichloromethane and dried over
anhydrous Na2SO4. After removal of the solvent, the residue was
purified by column chromatography (VCH2Cl2: VPE = 2:1) to afford
compound IVb as a yellow solid (0.25 g, 49%). m.p. 155–157 ꢀC; 1H
8.42 (s, 1H), 8.39 (d, J = 7.7 Hz, 1H), 8.32 (d, J = 8.5 Hz, 2H), 8.25 (d,
J = 8.5 Hz, 2H), 8.22 (dd, J = 8.6, 1.7 Hz, 1H), 8.18 (d, J = 2.9 Hz, 1H),
8.16 (d, J = 3.5 Hz, 1H), 7.98 (d, J = 6.8 Hz, 1H), 7.96 (d, J = 1.9 Hz, 1H),
7.68 (dd, J = 8.0, 1.9 Hz, 1H), 7.65 (d, J = 6.6 Hz, 1H), 7.62 (d, J = 8.6 Hz,
1H), 7.56–7.49 (m, 2H), 7.47–7.42 (m, 2H), 7.40 (d, J = 7.4 Hz, 1H),
7.37 (d, J = 6.5 Hz, 1H), 1.57 (s, 6H); 13C NMR (125 MHz, DMSO)
d:
NMR (500 MHz, CDCl3)
d
9.77 (s, 1H), 8.81 (d, J = 1.6 Hz, 1H), 8.45 (d,
165.36, 163.08, 155.31, 153.64, 153.20, 153.01, 140.94, 140.81,
140.30, 138.04, 137.67, 135.65, 134.03, 130.61 (2C), 129.73, 129.50
(2C), 129.09, 128.70, 127.71, 127.61, 127.11, 126.51, 125.45, 122.98,
122.80,122.74,121.45,121.23,121.20, 120.61,120.30, 120.25,116.24,
J = 7.5 Hz,1H), 8.29 (d, J = 7.8 Hz,1H), 8.11 (dd, J = 8.6,1.8 Hz,1H), 7.98
(d, J = 5.5 Hz, 1H), 7.97 (d, J = 4.2 Hz, 2H), 7.84 (d, J = 6.6 Hz, 1H), 7.69
(d, J = 1.8 Hz, 1H), 7.64 (d, J = 8.6 Hz, 1H), 7.60 (dd, J = 7.9, 1.9 Hz, 1H),
7.53-7.51 (m, 2H), 7.50-7.48 (m, 2H), 7.44 ꢂ7.41 (m, 2H), 7.39-7.36
(m, 1H), 1.60 (s, 6H).
115.37, 109.88, 109.72, 104.47, 78.42, 46.78, 26.58; IR n
/cmꢂ1 (KBr)
3445.4, 2921.87, 2518.91, 2228.91, 2141.06, 1796.65, 1596.69,
1546.44, 1461.69, 1358.41, 1232.14, 1090.6, 883.73, 734.04;
HRESIMS m/z 663.1887 [M-H]ꢂ, cacld C43H28N4O2S for:
664.1933; Elemental analysis calcd (%): C 77.69, H 4.25, N 8.43;
Found (%):C 78.05, H 4.45, N 8.05.
2.4.7. Synthesis of 2-cyano-3-[5-[7-(9-(9,9-dimethyl-9H-fluoren-2-
yl)-9H-carbazol-3-yl)-2,1,3-benzothiadiazol-4-yl]-2-furanyl]- 2-
propenoic acid LY-F
To
a solution of compound IVb (0.2 g, 0.34 mmol) and
cyanoacetic acid (0.06 g, 0.7 mmol) in THF (20 mL), piperidine
(0.16 mL) was added. The mixture was refluxed for 12 h. Then the
solvent was removed in vacuo and the residue was purified by
column chromatography (VCH2Cl2: VCH3OH: VHAc = 400: 8: 2) to
afford compound LY-F as a purple solid (0.153 g, 69%). m.p. 259–
2.4.10. Synthesis of 5-(9-(9,9-dimethyl-9H-fluoren-2-yl)-9H-
carbazol-3-yl)-2-thiophenecarboxaldehyde Va
A mixture of compound II (1.74 g, 4.00 mmol), (5-formylth-
iophen-2-yl)boronic acid (0.69 g, 4.4 mmol), Pd(PPh3)4 (0.46 g,
0.40 mmol), aqueous K2CO3 (2 M, 7 mL) in THF (18 mL) was refluxed
for 10 h under N2 atmosphere. The reaction was quenched with
water. The reactant was extracted with dichloromethane and dried
over anhydrous Na2SO4. After removal of the solvent, the residue
was purified by column chromatography (VCH2Cl2: VPE = 2:1) to
262 ꢀC; 1H NMR (500 MHz, DMSO)
d: 9.04 (d, J = 1.6 Hz, 1H), 8.39 (t,
J = 7.8 Hz, 2H), 8.28 (dd, J = 8.7, 1.8 Hz, 1H), 8.24 (d, J = 7.6 Hz, 1H),
8.21 (s, 1H), 8.16 (d, J = 8.0 Hz, 1H), 7.98 (d, J = 3.9 Hz, 2H), 7.95 (d,
J = 1.9 Hz, 1H), 7.70 (d, J = 3.7 Hz, 1H), 7.67 (dd, J = 8.0, 1.9 Hz, 1H),
7.64 (d, J = 6.7 Hz, 1H), 7.60 (d, J = 8.6 Hz, 1H), 7.54-7.49 (m, 2H),
7.45-7.40 (m, 2H), 7.40-7.36 (m, 1H), 1.59 (s, 6H); 13C NMR
afford compound Va as
a yellow solid (0.59 g, 31%). m.p.
224 ꢃ 226 ꢀC; 1H NMR (500 MHz, CDCl3)
d 9.91 (s, 1H), 8.48 (d,
(125 MHz, DMSO)
d
:163.70, 155.28, 154.39, 153.66, 153.07, 150.93,
J = 1.6 Hz, 1H), 8.23 (d, J = 7.8 Hz, 1H), 7.96 (d, J = 7.9 Hz, 1H), 7.83 (d,
J = 7.0 Hz,1H), 7.79 (d, J = 3.9 Hz,1H), 7.77 (dd, J = 8.5,1.8 Hz,1H), 7.63
(d, J = 1.7 Hz, 1H), 7.55-7.51 (m, 2H), 7.50-7.49 (m, 4H), 7.42 (td,
J = 6.6, 1.1 Hz, 2H), 7.40-7.36 (m, 1H), 1.59 (s, 6H).
147.44, 140.69, 140.24, 140.22, 138.00, 137.74, 135.60, 134.41,
128.25, 127.67, 127.27, 127.21, 126.50, 126.02, 125.35, 123.01,
122.88(2C), 121.46, 121.39, 121.17, 121.11, 120.70, 120.40, 118.63,

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2.4.11. Synthesis of 2-cyano-3-[5-(9-(9,9-dimethyl-9H-fluoren-2-yl)-
9H-carbazol-3-yl)-2-thienyl]- 2-propenoic acid LT-S
J = 6.1, 3.0 Hz,1H),1.59 (s, 6H). HRESIMS m/z 464.2014 [M+H]+, cacld
34H25NO for: 463.1936
C
Compound LT-S was synthesized through the method reported
by Ref [27] as a purple solid (0.22 g, 74%). m.p. 276–278 ꢀC; 1H NMR
2.4.15. Synthesis of 2-cyano-3-[4-(9-(9,9-dimethyl-9H-fluoren-2-yl)-
9H-carbazol-3-yl)phenyl]- 2-propenoic acid LT-P
(500 MHz, DMSO)
d 13.78 (bs, 1H, COOH), 8.79 (s, 1H), 8.51 (s, 1H),
8.43 (t, J = 7.8 Hz, 1H), 8.15 (d, J = 8.0 Hz, 1H), 8.07 (d, J = 3.7 Hz, 1H),
7.97 (d, J = 7.3 Hz, 1H), 7.91 (d, J = 6.1 Hz, 2H), 7.86 (d, J = 3.8 Hz, 1H),
7.63 (d, J = 7.3 Hz, 2H), 7.53 (t, J = 7.0 Hz, 2H), 7.47-7.36 (m, 4H), 1.54
(s, 6H).
To a solution of compound Vc (0.93 g, 2.00 mmol) and cyano-
acetic acid (0.35 g, 4.00 mmol) in THF (20 mL), piperidine (0.75 mL)
was added. The mixture was refluxed for 12 h. Then the solvent was
removed in vacuo and the residue was purified by column
chromatography (VCH2Cl2: VCH3OH: VHAc = 400: 4: 1) to afford
compound LY-P as a yellow solid (0.93 g, 88%). m.p. 268–270 ꢀC; 1H
2.4.12. Synthesis of 5-(9-(9,9-dimethyl-9H-fluoren-2-yl)-9H-
carbazol-3-yl)-2-furancarboxaldehyde Vb
NMR (500 MHz, DMSO)
d 14.0 (bs, 1H, COOH), 8.81 (s, 1H), 8.41 (d,
A mixture of compound II (1.10 g, 2.5 mmol), (5-formylfuran-2-
yl)boronic acid (0.55 g, 3.75 mmol), Pd(PPh3)4 (0.29 g, 0.25 mmol),
aqueous K2CO3 (2 M, 5 mL) in THF (30 mL) was refluxed for 10 h
under N2. The reaction was quenched with water. The reactant was
extracted with dichloromethane and dried over anhydrous Na2SO4.
After removal of the solvent, the residue was purified by column
chromatography (VCH2Cl2: VPE = 2:1) to afford compound Vb as a
pink solid (0.6 g, 53%). m.p. 135 ꢃ137 ꢀC; 1H NMR (500 MHz, CDCl3)
J = 8.3 Hz, 2H), 8.20 (d, J = 7.9 Hz, 2H), 8.14 (d, J = 7.9 Hz, 1H), 8.08 (d,
J = 7.9 Hz, 2H), 7.97–7.92 (m, 3H), 7.63 (d, J = 7.1 Hz, 2H), 7.55–7.46
(m, 3H), 7.44–7.35 (m, 3H), 1.55 (s, 6H); 13C NMR (125 MHz, DMSO)
d
163.64, 155.38, 153.83, 153.71, 145.21, 140.87, 140.47, 138.11,
137.75, 135.62, 131.52 (2C), 130.53, 129.70, 127.72, 127.24, 127.07
(2C), 126.72, 125.50, 125.38, 123.56, 122.88 (2C), 121.58, 121.30,
120.45 (2C), 120.40, 119.27, 116.42, 110.38, 109.99, 102.51, 46.88,
26.64 (2C); IR
n
/cmꢂ1 (KBr) 3447.29, 2959.11, 2226.7, 1795.46,
d
9.67 (s, 1H), 8.69 (d, J = 1.6 Hz, 1H), 8.25 (d, J = 7.7 Hz, 1H), 7.96 (d,
1696.33, 1583.03, 1463.49, 1423.44, 1365.28, 1275.15, 1232.06,
J = 8.0 Hz, 1H), 7.89 (dd, J = 8.6, 1.6 Hz, 1H), 7.83 (d, J = 10.7,
4.0 Hz,1H), 7.64 (d, J = 1.8 Hz, 1H), 7.55 (dd, J = 7.9, 2.0 Hz, 1H),
7.53–7.51 (m, 2H), 7.50-7.47 (m, 2H), 7.45–7.40 (m, 2H), 7.40–7.36
(m, 2H), 6.89 (d, J = 3.8 Hz, 1H), 1.58 (s, 6H); HRESIMS m/z 454.1808
[M+H]+, cacld C32H23NO2 for: 453.1729
1189.37, 799.35, 738.88; HRESIMS m/z 529.1923 [M-H]ꢂ, cacld
C37H26N2O2 for: 530.1994; Elemental analysis calcd (%): C 83.75, H
4.94, N 5.28; Found (%):C 83.36, H 4.78, N 4.92.
3. Results and discussion
2.4.13. Synthesis of 2-cyano-3-[5-(9-(9,9-dimethyl-9H-fluoren-2-yl)-
9H-carbazol-3-yl)-2-furanyl]-2-propenoic acid LT-F
3.1. Synthesis
To
a
solution of compound Vb (0.23 g, 0.50 mmol) and
The synthetic pathway of carbazole dyes is depicted in
cyanoacetic acid (0.09 g, 1.00 mmol) in THF (20 mL), piperidine
(0.19 mL) was added. The mixture was refluxed for 12 h. Then the
solvent was removed in vacuo and the residue was purified by
column chromatography (VCH2Cl2: VCH3OH: VHAc = 400: 4: 1) to
Scheme 1. N-(dimethylfluorenyl)carbazole I was synthesized
through the substitution reaction of carbazole on N atom by 2-
bromo-9,9-dimethyl-9H-fluorene under the catalysis of Pd(OAc)2.
The bromide II, obtained through the bromination of I with NBS,
reacted with formylarylboronic acids through Suzuki coupling
reaction to give the intermediate aldehydes V. LT-series dyes were
synthesized through the condensation of V with cyanoacetic acid.
Bromide II was coupled with 4,7-dibromobenzothiadiazole to form
the intermediate III. The second Suzuki coupling was occurred
between III and formylarylboronic acids to afford the aldehydes IV.
IV reacted with cyanoacetic acid to produce LY-series dyes.
afford compound LY-F as
a red solid (0.16 g, 62%). m.p.
278 ꢃ 280 ꢀC; 1H NMR (500 MHz, DMSO)
d 13.61 (bs, 1H, COOH),
8.87 (s, 1H), 8.22 (d, J = 7.8 Hz, 1H), 8.11 (dd, J = 8.0, 3.5 Hz, 1H), 8.08
(d, J = 2.0 Hz, 1H), 8.04 (dd, J = 8.7, 1.7 Hz, 1H), 7.95 (d, J = 6.7 Hz, 1H),
7.91 (t, J = 2.3 Hz, 1H), 7.63–7.60 (m, 3H), 7.54–7.49 (m, 2H), 7.47 (d,
J = 8.4 Hz, 1H), 7.42–7.38 (m, 4H), 1.53 (s, 6H); 13C NMR (125 MHz,
DMSO)
d 165.66 (2C), 164.16, 160.19, 155.40, 153.71, 147.09, 140.99,
140.89, 138.30, 137.73, 135.27, 127.78, 127.26, 127.16, 127.1, 125.56,
123.59, 123.28, 122.90 (2C), 122.50, 121.63, 121.35, 120.85, 120.50,
115.58 (2C), 110.62, 110.32, 108.76, 95.90, 46.92, 26.63, 24.62; IR
3.2. Optical properties
n
/cmꢂ1 (KBr) 3444.67, 2958.98, 2218.47, 1723.37, 1678.52, 1599.05,
The UV–vis spectra of the carbazole dyes in CHCl3-CH3OH
solution are displayed in Fig. 1(a) and (b), and the corresponding
data are summarized in Table 1. LT-series dyes exhibit two
absorption peaks: one peak at about 310 nm is ascribed to
transition and the other peak is found at 350–400 nm caused by
1534.39, 1455.57, 1284.32, 1229.91, 1132.4, 1046.12, 885.86, 805.26,
742.54; HRESIMS m/z 519.1722 [MꢂH]ꢂ, cacld C35H24N2O3 for:
520.1787; Elemental analysis calcd (%): C 80.75, H 4.65, N 5.38;
Found (%):C 81.07, H 5.03, N 5.17.
p
!
p*
intramolecular charge transfer from the carbazole donor to the
2.4.14. Synthesis of 4-(9-(9,9-dimethyl-9H-fluoren-2-yl)-9H-
carbazol-3-yl)-benzaldehyde Vc
cyanoacrylic acid acceptor through p-bridge (Fig. 1(a)). After the
introduction of benzothiadiazole, ICT absorption peaks of LY-series
dyes shift bathochromically about 100 nm when compared with
LT-series dyes and the responsive wavelength of LY-series dyes is
extended to 550–600 nm from 500 nm of LT-series dyes (Fig. 1(e)).
A mixture of compound II (1.66 g, 3.79 mmol), (4-formylphenyl)
boronic acid (0.66 g, 4.40 mmol), Pd(PPh3)4 (0.44 g, 0.38 mmol),
aqueous K2CO3 (2 M, 7.5 mL) in THF (18 mL) was refluxed for 10 h
under N2 atmosphere. The reaction was quenched with water. The
reactant was extracted with dichloromethane and dried over
anhydrous Na2SO4. After removal of the solvent, the residue was
purified by column chromatography (VCH2Cl2: VPE = 2:1) to afford
compound Vc as a yellow solid (0.93 g, 53%). m.p. 200–202 ꢀC; 1H
Moreover, an additional peak between the
p
!
p* and ICT
absorption peak is observed at 350–400 nm which benefits blue
light harvesting of LY-series dyes. Therefore, the incorporation of
BTZ facilitates the efficient ICT and expands the light absorption
region, improving the light-harvesting capabilities of LY-series
dyes.
NMR (500 MHz, CDCl3)
d 10.10 (s, 1H), 8.46 (d, J = 1.6 Hz, 1H), 8.25
(d, J = 7.8 Hz, 1H), 8.02 (d, J = 8.0 Hz, 2H), 7.97 (d, J = 8.0 Hz, 1H), 7.92
(d, J = 8.2 Hz, 2H), 7.84 (dd, J = 6.6, 1.4 Hz, 1H), 7.75 (dd, J = 8.6, 1.8 Hz,
1H), 7.66 (d, J = 1.8 Hz, 1H), 7.59–7.55 (m, 2H), 7.53–7.49 (m, 3H),
7.45 (dd, J = 7.3, 1.3 Hz, 1H), 7.42 (dd, J = 7.3, 1.5 Hz, 1H), 7.37 (td,
On the other hand, in these carbazole dyes, the incorporation of
the electron-rich furan or thiophene bridge leads to the bath-
ochromic shift of lmax by ꢃ40 nm along with the distinct
broadening of the absorption spectra when compared with dyes
bearing benzene bridge. Replacement of furan with thiophene has